Journal of Marine Science and Engineering

The estimates of hydrodynamic forces for a group of structures represent a challenge for the design of offshore systems, as they are subject to changes with a variation in flow profiles. The fluctuating effects may be more pronounced or, on the contrary, suppressed if the cross-sectional shape of structures in an array is altered. The present work performs a series of 2D numerical simulations for the flow past six identical stationary cylinders of three distinct geometrical shapes arranged in a 2 × 3 matrix configuration. The flow profiles considered have an averaged velocity corresponding to the critical flow regime of a Reynolds number of 2.5 × 10⁵. The detached eddy simulation k–ω SST turbulence model is employed to perform a comprehensive investigation of the fluid force coefficients, their frequencies and vortex formation patterns. The effect of the spacing ratio varied simultaneously among the structures from 2 to 7 is considered in conjunction with the change in the flow profile and the cylinders’ cross-section. The results of simulations show a higher mean drag on the upstream cylinders, reduced mean drag on the mid- and downstream cylinders with the second cross-sectional shape, and a higher mean drag on the cylinders with the third cross-sectional shape, compared to the original circular cylinders. Full article

A broader application of biocomposites still faces many challenges regarding structural integrity, environmental resistance, and biodegradability. These issues are particularly important when their marine applications are considered. Therefore, this paper seeks to address the hygroscopicity, mechanical properties, and biofouling resistance of biocomposites made of epoxy resin with 28 m% bio-based carbon content reinforced with flax and hemp fibers. A series of experiments are performed to acquire water absorption rates, saturation limits, mass increase, tensile and flexural properties, interlaminar shear strength, impact resistance, and mass gain due to biofouling. All tests of mechanical properties are conducted before and after immersion in seawater. The acquired saturation limits of flax/epoxy and hemp/epoxy biocomposites amount to 7.5% and 9.8%, respectively. The water uptake causes the tensile and flexural properties to decrease by 26–74%, while interlaminar and impact strength increase for flax/epoxy and decrease for hemp/epoxy biocomposites. In addition, it is observed that in almost all cases, flax/epoxy has superior properties compared with hemp/epoxy biocomposites. It is expected that this research will motivate naval architects and classification societies to consider biocomposites as prospective hull materials that provide both structural integrity and environmental sustainability. Full article

Spatial environmental heterogeneity in the Yangtze River Estuary (YRE) is always mentioned but rarely quantified and included in the evaluation process. This study introduced the habitat suitability index evaluation model based on the Gini index (HSI_gini) to evaluate the optimal ranges of suitable environmental factors for three typical estuarine gobies, i.e., Rhinogobius giurinus, Acentrogobius pflaumii, Odontamblyopus rubicundus, and their habitat quality. The evaluation was carried out based on field surveys conducted in the spring and summer of 2018–2020. The Lorentz curve and Gini index were used to evaluate the spatial environmental heterogeneities in the YRE. The spatial heterogeneity of environmental factors in the Yangtze Estuary ranged from 0.62 to 0.05, with the highest Gini index for salinity and the lowest for temperature. The combination of environmental factors had significant spatial effects on habitat, with temperature showing mainly seasonal effects. The study indicated that the YRE is a good habitat for gobies and that there is spatial and seasonal differentiation in the habitats of different species, greatly reducing interspecific competition. Environmental heterogeneity is important for biological processes and should be incorporated into the modeling of bio–environmental relationships in future research to provide a basis for environmental and biological conservation and management. Full article

Despite the great utility of nanoparticles (NPs) in water remediation, their effects on marine ecosystems are unknown and unpredictable. The toxicity of the most used nanoparticles, such as ZnO, Ag, and TiO₂ on the purple sea urchin, Paracentrotus lividus (Lamarck, 1816), has been demonstrated by several authors. The aim of this study was to evaluate the effects of TiO₂ sol-gel and TiO₂-rGO nanocompounds on both vitality and motility of spermatozoa of P. lividus. The spermatozoa were exposed at different times (30 and 60 min) and concentrations (10, 20, 40 µg/mL) of both nano-TiO₂ compounds. The results clearly showed a decrease in both vitality and motility of P. lividus spermatozoa exposed. In particular, vitality and motility were inversely related to both exposure time and concentration of TiO₂ sol-gel and TiO₂-rGO nanocompounds. Full article

Tsunamis can cause high numbers of casualties, as well as direct and indirect economic losses to coastal regions. The huge destructiveness of tsunamis requires us to study tsunami risk and its temporal change. We adopt the tsunami scenarios of the Ryukyu Trench as an example to analyze the temporal change in tsunami risk. According to the tsunami numerical model results, the tsunami inundation in the worst tsunami scenario covered an area of 82.83 km². Satellite data including Landsat 8 images from July 2013 and Landsat 9 images from March 2022 were used with the random forest (RF) method to analyze land use and tsunami vulnerability in 2013 and 2022. The tsunami risk and its temporal change were analyzed by integrating tsunami hazard and tsunami vulnerability. The tsunami risk change analysis results show that the area of tsunami risk level 1 increased by 4.57 km², and the area of tsunami risk level 4 decreased by 7.31 km². By analyzing changes in land use and land cover (LULC) and tsunami risk, we concluded that the expansion of constructed land and the increase in coastal population were responsible for the increase in tsunami risk. The results of tsunami risk change analysis will help us understand the current tsunami risk and predict possible future risk change. In addition, it is necessary to prepare tsunami prevention measures in advance and produce tsunami emergency response plans for Qidong County and other regions under potential tsunami threat. Full article

Based on four years of spatially synchronous topographic data of the Oujiang Estuary from 2002 to 2019, the variations and physical mechanisms of estuarine evolution driven by natural conditions and human activities since the beginning of this century were analyzed. The results show that the evolution of the Oujiang Estuary has changed dramatically in the past 20 years. From 2002 to 2019, the net sediment erosion of the estuary was 163.44 million m³, and the average bed elevation of the river-dominated section (RDS), transition section (TS) and tide-dominated section (TDS) decreased by 4.61 m, 1.30 m and 2.14 m, respectively. In addition, the pattern of the shoal channel had changed, and the river facies coefficient (width–depth ratio) decreased by 16–64%. The evolution of the Oujiang Estuary is mainly caused by human activities (such as sand mining, reclamation). Sand mining is the direct cause of riverbed undercutting, and the large undercutting of riverbed terrain causes the increase in tidal power in the estuary and further causes river channel scouring. In the last 20 years, the average annual tidal range of the estuary increased by 0.19–1.14 m, and the flood discharge increased by about 17–80%, with an average value of 58%. The impact of tidal power on the evolution and development of the estuary has increased significantly. Apart from sand mining, reclamation projects such as the Wenzhou shoal outside the mouth also cause the local velocity of the tidal current section to increase, which aggravates the scouring trend of local river sections downstream. The scouring and silting changes in the Oujiang Estuary since the beginning of this century are the result of the adjustment of the estuarine system in response to the strong intervention of human activities. Full article

A series of numerical simulations of two-degree-of-freedom vortex-induced vibration of two coupled cylinders with unequal diameters are performed at the Reynolds number of 20,000. The effects of incident angle, spacing ratio, and diameter ratio on the VIV responses for two cylinders are investigated. It is shown that the lock-in range of the large cylinder is significantly widened and the maximum vibration amplitude decreases as a result of the existence of small cylinder. The mean drag coefficients and root mean square force coefficients of the large cylinder are not varied significantly with the incident angle and diameter ratio, but the force coefficients of the small cylinder vary considerably under different configurations. For the configuration of α = 0°, d/D = 0.05 and G/D = 0.05, the variations in vibration amplitude and frequency ratio are similar to those of the isolated cylinder. Different vortex shedding modes such as 2S mode, P+S mode, and 2P mode are observed for two coupled cylinders at different reduced velocities for different configurations. Full article

CO₂-N₂-mixture injection can be used for the exploitation and reformation of natural gas hydrate reservoirs. The permeability evolution of sediments in the presence of CO₂-N₂ hydrate is very important. In current permeability tests, hydrate-bearing sediment formed from CO₂-N₂ gas mixture is rarely involved. In this work, hydrate-bearing sediment was formed from CO₂-N₂ mixtures, and a constant flow method was employed to measure the permeability of the hydrate-bearing sediments. The effects of CO₂ mole fraction and hydrate saturation on the permeability were investigated. The results show that gas composition is the key factor affecting hydrate formation. Hydrate saturation increases with increasing CO₂ mole fraction in the gas mixture. The presence of hydrate formed from a CO₂-N₂ mixture leads to a sharp permeability reduction. The higher the fraction of CO₂ in the injected gas mixture, the lower the sediment’s permeability. Our measured permeability data were also compared with and fitted to prediction models. The pore-filling model underestimates the permeability of hydrate-bearing sediments formed from a CO₂-N₂ gas mixture. The fitted hydrate saturation index in the Masuda model is 15.35, slightly higher than the general values, which means that the formed hydrates tend to occupy the pore center, and even block the pore throat. Full article

Submarine volcanic eruptions can be destructive for marine environments and resources. Magma mixing is considered to be an important trigger for volcanic eruptions. Determining the magma residence time from mixing to eruption is conducive to assessing the stability of magmatic systems, especially beneath the seafloor where in situ volcano monitoring is inaccessible. Here, we estimated the timescale of magma mixing beneath the Iheya Ridge, Okinawa Trough, which is characterized by pervasive magma mixing. We focused on andesitic and rhyolitic magma generated by basalt–rhyolite mixing and rhyolite–rhyolite mixing, respectively. By taking advantage of the Mg diffusion chronometry, we showed that the andesitic magma resided in the magma chamber for very short time (~0.1–0.3 years), whereas the residence time of the rhyolitic magma was much longer (~80–120 years). The different times might be in part related to the different rheology of the mixed magmas. The short residence time of the andesitic magma suggested efficient magma mixing that allowed the andesites to be erupted, which may explain the appearance of scarce andesites in basalt–rhyolite dominant settings. However, the rapid mixing and eruption of magma is a disadvantage for the development and preservation of seafloor hydrothermal resources. Therefore, we suggest that the stability of sub-seafloor magma systems must be evaluated during the assessment of seafloor sulfide resources and mining prospects. Full article

An acoustic experiment to measure the sound field during internal wave activity was conducted in the South China Sea. During the experiment, a train of strong internal solitary waves (ISWs) moved from the acoustic source to the receiver array along the acoustic path, and the propagation direction of the ISWs train was almost parallel to the acoustic path. Here, a study of the characteristics and physical mechanisms of the acoustic temporal coherence in this scenario is reported. The temporal coherence was analyzed by using the simulation results and experimental data. The results show that the temporal correlation coefficients oscillate quasi-periodically with both time and time delay, and the predominant oscillation periods are the same as the periods of the ISWs. The predominant fluctuation frequencies of the sound field correspond to some specific modes and lead to the periodicity of the temporal correlation coefficients. In the shallow layer, the spectrum structures of the temporal correlation coefficients are simpler because of the fewer effective modes. Full article

The box girder can be seen as a kind of simplified ship structure that can withstand a vertical bending moment. Dynamic loads play an important role in structural safety analysis, such as ship bow slamming during harsh sea conditions. In this paper, the dynamic elastic–plastic response and ultimate strength of a box girder under a bending moment are analyzed. A box girder with the same cross-section scantlings and span length as the Nishihara experiment is selected as the analysis object. Based on the model experiment results, the non-linear FE analysis method is validated to capture the ultimate strength of a box girder under bending moment. Then, six box girders were designed to study the critical influence factors on the dynamic ultimate moment, including the model length, plate thickness, mass density and load excitation period. On the basis of structural dynamic response, an evaluation criterion of dynamic limit state for the box girder under a bending moment is proposed in this paper. Compared with the static ultimate moment, the change in the dynamic ultimate moment is discussed in detail to obtain the general principal method for dynamic strength analysis. The conclusions in this paper can provide guidance for dynamic ultimate strength evaluation. Full article

Due to the limited energy in underwater sensor networks, underwater nodes need to be deployed sparsely. However, sparse USNs will lead to poor tracking coverage and detection capability. To solve these problems, the mobility of nodes in depth can be utilized to optimize the node topology to achieve data fusion more reliably and effectively. In this paper, for underwater target tracking, a node depth adjustment algorithm is proposed. Firstly, after introducing the sound velocity profile on acoustic signal transmission, the asynchronous particle filter algorithm based on delay estimation is improved, which makes the filter more suitable for an underwater environment. Secondly, the influence of node topology on the tracking accuracy is analyzed, and the optimization problem of node depth adjustment is constructed, in which the depth-related Fisher Information Matrix is designed as the optimization criterion. Thirdly, for scenarios in which the target depth is either known or unknown, the analytical method and the interior point method are employed to solve the problem, respectively, and the optimal depth adjustment strategies in corresponding scenarios are obtained. The simulation results show that the proposed algorithm can fully adjust the node depth and achieve a more accurate tracking performance. Full article

Ventilation ducts with a high cross-sectional area are frequently built as structural ducts that include inside transversal structural beams. In this way, the cross-sectional area requested is respected, but the transverse structural elements will have a big impact on the airflow, with eventually additional noise and vibration and a high amount of energy wasted across the beams. From this perspective, the aim of this study is to evaluate the impact of the transversal beams inside the ventilation ducts, to analyze different alternatives for airflow improvement using computational fluid dynamics (CFD) simulation, and to check the simulation results in the wind tunnel with an experimental model. The results of the experimental measurements have highlighted the high-pressure drop and, consequently, the high energy wasted across the transversal structural beams. It was found that the airflow downstream of the beam is changing the flow direction, and high turbulences and vortices are initiated in the shadow of the beam. According to the CFD analysis, the ventilation system can be improved by adding airflow deflectors in the beam area. In this way, the high turbulences are reduced, the vortices and backflow are canceled, and the pressure losses across the beam area of the ventilation duct are reduced by up to 90% compared with the beam without a deflector. Therefore, the energy wasted in the beam area can be reduced by up to 90%. Full article

This paper investigates a fault-tolerant control problem for the dynamic positioning of unmanned marine vehicles based on a Takagi–Sugeno (T-S) fuzzy model using an integral sliding mode scheme. First, the T-S fuzzy model of an unmanned marine vehicle is established by taking the yaw angle variable range into account. An integral sliding mode control scheme combined with the ${\mathcal{H}}_{\infty }$ performance index is then developed to attenuate the initial influence of thruster faults and ocean disturbances. The unknown nonlinear function is approximated using a fuzzy logic system based on a representation of marine data, which provides a good tradeoff between resolution of the unknown nonlinear term approximation and computational complexity for marine engineering by adjusting the number of fuzzy logic system rules. In addition, the fault estimation information is utilized to design the sliding mode surface on the basis of an adaptive mechanism and a matrix full rank decomposition technique, which reduces conservatism. The validity of the proposed approach is finally demonstrated by an analysis of simulation results using a typical floating production vessel model. Full article

The Posidonia oceanica decline due to climate change and other anthropogenic pressures, such as chemical pollution, is well known in the scientific community. However, a comprehensive study of the full content of the organic micropollutants found in this significant seagrass has not yet been carried out. Second, an eco-friendly extraction procedure that does not require a large sample, preserves the seagrass’s ecological integrity and functions, and follows green-chemistry principles, is lacking. These information gaps represent the aims of this study. For this purpose, trials with diverse simple and affordable extraction methods to detect one of the most ubiquitous contaminants (polycyclic aromatic hydrocarbons or PAHs) were conducted. As a result, the use and validation of a polytron homogenizer and an ultrasonic bath were proposed for the extraction of priority PAHs from tissues of P. oceanica and marine sediments, respectively. Tissues (leaves and rhizomes) of P. oceanica and sediment samples were collected, extracted, and subjected to a thorough analysis, i.e., target, suspect, and unknown screenings, using gas chromatography coupled to high resolution mass spectrometry (GC-Q-Orbitrap MS). Target analysis revealed seven priority parent-PAHs, whilst during the suspect screening, four PAH-derivatives and three other parent-PAHs were tentatively identified. In the additional third unknown analysis, 11 structures, several with concerning toxicity, were also tentatively identified. Numerous of the identified compounds showed elevated detection frequency in the environmental samples, even reaching 100%, such as the cases of the parent-PAHs (naphthalene, phenanthrene and retene), some PAH-derivatives, one UV stabilizer, and plastic additives along with pesticides. The methods proposed here should be considered for future monitoring of P. oceanica, as well as the three-way analytic approach (target, suspect and unknown), to obtain a more real and accurate idea of the organic micropollutants content in the environment. Full article

With the passage of time, the exploitation of Internet of Things (IoT) sensors and devices has become more complicated. The Internet of Underwater Things (IoUT) is a subset of the IoT in which underwater sensors are used to continually collect data about ocean ecosystems. Predictive analytics can offer useful insights to the stakeholders associated with environmentalists, marine explorers, and oceanographers for decision-making and intelligence about the ocean, when applied to context-sensitive information, gathered from marine data. This study presents an architectural framework along with algorithms as a realistic solution to design and develop an IoUT system to excel in the data state of the practice. It also includes recommendations and forecasting for potential partners in the smart ocean, which assist in monitoring and environmental protection. A case study is implemented which addresses the solution’s usability and agility to efficiently exploit sensor data, executes the algorithms, and queries the output to assess performance. The number of trails is performed for data insights for the 60-day collection of sensor data. In the context of the smart ocean, the architectural design innovative ideas and viable approaches can be taken into consideration to develop and validate present and next-generation IoUTs and are simplified in this solution. Full article

Global change effects have favoured the introduction of new species in marine ecosystems in recent years. Gracilaria vermiculophylla, a red seaweed native from the north-eastern Pacific, has successfully colonised large regions in the Northern Hemisphere. In this research, we implemented species distribution models (SDMs) to (i) examine which were the most important environmental factors defining the presence of G. vermiculophylla at a global scale, and (ii) determine the potential current and future distribution of G. vermiculophylla based on two climate scenarios (representative concentration pathways (RCP 2.6 and RCP 8.5)). Our results suggest that temperature and salinity were the most important variables explaining the distribution of the target species. Additionally, the SDMs for present climate settings showed a potential wider distribution than is recorded to date. In addition, a subtle habitat expansion of 2.9° into higher latitudes was reported under the RCP 2.6 scenario by the end of this century. The high-carbon-emission scenario (RCP 8.5) delivered a potential large habitat expansion (6.0°), even reaching arctic latitudes, and a remarkable habitat loss of 11° in its southern distribution range. SMDs also forecasted suitable areas for this species in the Southern Hemisphere, pointing toward a potential global expansion in the coming decades. Full article

This article presents two new chemical plume tracing (CPT) algorithms for using on autonomous underwater vehicles (AUVs) to locate hydrothermal vents. We aim to design effective CPT navigation algorithms that direct AUVs to trace emitted hydrothermal plumes to the hydrothermal vent. Traditional CPT algorithms can be grouped into two categories, including bio-inspired and engineering-based methods, but they are limited by either search inefficiency in turbulent flow environments or high computational costs. To approach this problem, we design a new CPT algorithm by fusing traditional CPT methods. Specifically, two deep reinforcement learning (RL) algorithms, including double deep Q-network (DDQN) and deep deterministic policy gradient (DDPG), are employed to train a customized deep neural network that dynamically combines two traditional CPT algorithms during the search process. Simulation experiments show that both DDQN- and DDPG-based CPT algorithms achieve a high success rate (>90%) in either laminar or turbulent flow environments. Moreover, compared to traditional moth-inspired method, the averaged search time is improved by 67% for the DDQN- and 44% for the DDPG-based CPT algorithms in turbulent flow environments. Full article

The ship hull structure is composed of plates and stiffened panels. Estimating the maximum load-carrying capacity, or the ultimate strength, of these structural components is fundamental. One of the main challenges nowadays is the implementation of new materials and technologies to enhance the structural integrity, economy, safety and environmentally friendly design of the ship’s hull structure. A new design solution may be represented by aluminium alloy honeycomb sandwich structures, both as plane panels or stiffened ones, which are characterised by excellent impact-absorption capabilities and a high stiffness-to-weight ratio. Still, their response to some conditions typical of ship structural design needs to be deeply investigated. Axial compressive loading is one of the most critical conditions that could impact the structural integrity of such light-weight solutions. Hence, the uniaxial compressive behaviour of aluminium honeycomb sandwich structures has to be deeply investigated to promote their integration in ship structural design. Within this context, the present work performs an experimental and numerical study of a honeycomb sandwich panel subjected to uniaxial compressive loads. The results will help develop models for predicting the uniaxial compressive load-carrying capacity of hybrid honeycomb sandwiches of aluminium alloy design. Full article